This invention relates generally to semiconductor structures and devices and to a method for their fabrication, and more specifically to pyroelectric devices and integrated circuits fabricated on a monocrystalline material.
Various metallic oxides, such as perovskites, exhibit desirable characteristics such as piezoelectric, pyroelectric, ferroelectric, ferromagnetic, colossal magnetic resistance, and super conductivity properties. Such oxides may be included or used in connection with microelectronic devices that take advantage of these characteristics. For example, metallic oxides may be used to form pyroelectric imaging devices and the like.
For many years attempts have been made to grow thin films of various metallic oxide materials on a foreign substrate because of the desirable characteristics of the metallic oxide materials, and because of their present generally high cost and low availability in bulk form. To achieve optimal characteristics of metallic oxide material, however, a monocrystalline film of high crystalline quality is desired. Attempts have been made, for example, to grow layers of a monocrystalline metallic oxide material on substrates such as silicon. These attempts have generally been unsuccessful because lattice mismatches between the host crystal and the grown crystal have caused the resulting thin film of metallic oxide material to be of low crystalline quality. Metallic oxides of higher quality have been grown over oxide substrates such as bulk strontium titanate. Metallic oxides grown over oxide substrates are often expensive because, in part, the oxide substrate is small and expensive.
If a large area thin film of high quality monocrystalline metallic oxide material was available at low cost, a variety of semiconductor devices could advantageously be fabricated using that film at a low cost compared to the cost of fabricating such devices on a bulk wafer of the metallic oxide material or in an epitaxial film of such material on a bulk wafer of oxide material. In addition, if a thin film of high quality monocrystalline metallic oxide material could be realized on a bulk wafer such as a silicon wafer, an integrated device structure could be achieved that took advantage of the best properties of both the silicon and the metallic oxide material.
Several perovskite thin films are known to have at room temperature pyroelectric properties that are suitable for infrared detection devices. Pyroelectric detectors are designed to absorb infrared radiation that gives rise to a temperature increase which causes a change in the polarization of the pyroelectric materials. The change in polarization results in current production that can be detected by an integrated circuit. Critical factors for selecting a pyroelectric detector include pyroelectric current and response time. The sensitivity of a pyroelectric detector is primarily dependent on the magnitude of the pyroelectric coefficient, p, according to the equation:
I=pAxcex94T/xcex94t
where I is the current produced by the pyroelectric device, A is the area of the pyroelectric device, xcex94T is the change in temperature detected by the pyroelectric device and xcex94t is the change in time of a given measurement. The magnitude of the pyroelectric coefficient p is dependent on the crystalline quality of the pyroelectric materials. Monocrystalline films have a higher pyroelectric coefficient compared to polycrystalline films. Thus, the sensitivity of the temperature detection may increase and the device area may decrease while still maintaining the same sensitivity level.
Sandia National Laboratories has successfully integrated a polycrystalline Pb(Zr, Ti)O3 pyroelectric thin film into a CMOS architecture using an aerogel thermal isolation layer. See xe2x80x9cInvestigation of PZT//LSCO//Pt//Aerogel Thin Film Composites For Uncooled Pyroelectric IR Detectors,xe2x80x9d Mat. Res. Soc. Symp., Vol. 541, pg. 661 (1999). However, the integration of monocrystalline pyroelectric thin films using PZT, Pb(Se, Ta)O3 and other perovskite films on a substrate, has not been obtained.
Accordingly, a need exists for a pyroelectric detection device formed using a thin film of high quality monocrystalline oxide material formed on a bulk wafer. A need further exists for a thin film perovskite pyroelectric detection device that is monolithically integrated with a CMOS device on a monocrystalline substrate and that does not require cooling to operate.